U.S. patent number 6,488,770 [Application Number 09/719,036] was granted by the patent office on 2002-12-03 for monocrystalline powder and monograin membrane production.
This patent grant is currently assigned to Forschungszentrum Julich GmbH. Invention is credited to Mare Altosaar, Dieter Meissner, Enn Mellikov.
United States Patent |
6,488,770 |
Meissner , et al. |
December 3, 2002 |
Monocrystalline powder and monograin membrane production
Abstract
For production of monocrystalline powders there is formed a melt
to which a fluxing agent is added. The melt contains the components
of a semiconductor material, an example being the components of
copper indium diselenide which are generally used in a
stoichiometric composition. The melt is usually heated to
temperatures of between 300.degree. C. and 1000.degree. C.
Monocrystalline powder grains grow. The desired recrystallization
takes place at temperatures above the melting points of the
materials to be fused. Once the powder grains have the desired
size, the growth is stopped by quenching. The appropriate instant
of quenching as well as the appropriate temperature profile for
obtaining desired powder sizes are determined by, for example,
preliminary experiments. Thereafter the fluxing agent is
eliminated. Monograin membranes are produced from the powders
produced according to the process and are used in particular in
solar cells. The process is simple and inexpensive. Powder grains
of uniform size are obtained.
Inventors: |
Meissner; Dieter (Linz,
AT), Mellikov; Enn (Saku, EE), Altosaar;
Mare (Tallin, EE) |
Assignee: |
Forschungszentrum Julich GmbH
(Julich, DE)
|
Family
ID: |
7871979 |
Appl.
No.: |
09/719,036 |
Filed: |
December 6, 2000 |
PCT
Filed: |
June 23, 1999 |
PCT No.: |
PCT/DE99/01870 |
PCT
Pub. No.: |
WO99/67449 |
PCT
Pub. Date: |
December 29, 1999 |
Foreign Application Priority Data
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Jun 25, 1998 [DE] |
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198 28 310 |
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Current U.S.
Class: |
117/73; 117/74;
117/75; 117/77; 117/78 |
Current CPC
Class: |
C30B
9/00 (20130101); C30B 29/40 (20130101); C30B
29/46 (20130101); C30B 29/60 (20130101) |
Current International
Class: |
C30B
9/00 (20060101); C30B 007/08 () |
Field of
Search: |
;117/73,74,75,77,78 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 004 339 |
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Aug 1970 |
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DE |
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173 641 |
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Mar 1986 |
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EP |
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WO 89/05280 |
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Jun 1989 |
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WO |
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Other References
Altosar et al., "Monograin Layers and Membranes for Photovoltaics",
Conf. Record of the 25.sup.th IEEE Photovoltaic Specialists
Conference, May 13-17, 1996, 877-880. .
T.S. te Velde and G.W.M.T. van Helden, "Monograin Layers", Philips
Technical Review, 29 (1968), 238-242..
|
Primary Examiner: Kunemund; Robert
Attorney, Agent or Firm: Frishauf, Holtz, Goodman &
Chick, P.C.
Claims
What is claimed is:
1. A process for production of a monocrystalline powder comprising
a semiconductor material, the process comprising: (a) fusing
together individual components of the semiconductor material or
salts of the components to form a melt, (b) adding a fluxing agent
to the melt, (c) adjusting the temperature of the melt together
with the fluxing agent contained therein such that the components
or their salts melt and at the same time the powder to be produced
crystallizes out, so that monocrystalline powder grains grow, and
(d) cooling the melt by rapidly quenching the melt such that the
growth of the monocrystalline powder grains is stopped.
2. The process according to claim 1, wherein the fluxing agent is
eliminated after the cooling.
3. The process according to claim 1, wherein the fluxing agent is
selected from the group consisting of NaCl, Se, As, an arsenide and
a selenide.
4. The process according to claim 1, wherein the fluxing agent is
contained in the melt in a proportion of 10 vol % to 90 vol %.
5. The process according to claim 1, wherein the semiconductor
material comprises a Group II/VI semiconductor or a Group III/V
semiconductor.
6. The process according to claim 2, wherein the fluxing agent is
selected from the group consisting of NaCl, Se, As, an arsenide and
a selenide.
7. The process according to claim 2, wherein the fluxing agent is
contained in the melt in a proportion of 10 to 90 vol %.
8. The process according to claim 3, wherein the fluxing agent is
contained in the melt in a proportion of 10 to 90 vol %.
9. The process according to claim 6, wherein the fluxing agent is
contained in the melt in a proportion of 10 to 90 vol %.
10. The process according to claim 2, wherein the semiconductor
material comprises a Group II/VI semiconductor or a Group III/V
semiconductor.
11. The process according to claim 2, wherein the semiconductor
material comprises copper indium diselenide or GaAs.
12. The process according to claim 11, wherein in step (b), the
temperature is 300.degree. C. to 1000.degree. C.
13. The process according to claim 1, wherein the semiconductor
material is selected from the group consisting of CdTe, CdSeTe,
CdS, CdSSeTe, GaAs, InP and CuSeIn.
14. The process of claim 1, wherein the quenching is carried out in
a few seconds.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application is a U.S. National Phase Application under 35 USC
371 of International Application PCT/DE99/01870 (not published in
English) filed Jun. 23, 1999.
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a process for production of
monocrystalline powders and a monogram membrane comprising the
same.
BACKGROUND INFORMATION
A monogram membrane is a thin film constructed from one layer of
powder. The powder grains are bonded together.
From the article entitled "Monograin layers" by T. S. Velde and G.
W. M. T. van Helden in Philips Technical Review, 29 (1968),
238-242, it is known that a monogram membrane can be produced from
monocrystalline CdS powder. Monocrystalline powder comprising CdS
is obtained by crushing a relatively large single crystal. A
bonding agent is then applied as a thin film on a glass substrate.
The powder is scattered on the film of the bonding agent. Thereupon
a layer of the powder adheres to the bonding agent. The other
powder grains not attached to the bonding agent are eliminated.
Dissolved resin, polymer or components for the same are added to
the powder grains adhering to the bonding agent. After the solution
has been dried and cured, the film containing a powder layer is
peeled from the substrate. If necessary, the powder grains can be
exposed by etching, starting from the surface. Otherwise the powder
grains are or remain held together by the resin, etc. and thus form
the desired monogram membrane.
One problem is the production of the monocrystalline powder. For
example, it is relatively expensive first of all to produce a
relatively large single crystal. It is also hardly possible to
produce powder grains of uniform size by mechanical crushing.
Powder grains of uniform size are necessary in order to obtain a
monogram membrane of uniform thickness.
A monogram membrane can be used advantageously in the art of
photovoltaics, among others. Copper indium diselenide is a
particularly suitable material for this purpose.
SUMMARY OF THE INVENTION
The object of the invention is to provide an inexpensive process
for production of monocrystalline powder with predetermined grain
sizes. A further object of the invention is to provide, for the
first time, particular monogram membranes comprising powders formed
according to the process.
The objects are achieved by a process having the features described
hereinbelow as well as by a monogram membrane having the features
described hereinbelow. Advantageous embodiments are specified
hereinbelow.
The present invention concerns a process for producing a
monocrystalline powder comprising a semiconductor material. The
process comprises: (a) fusing together individual components of the
semiconductor material or salts thereof to form a melt; (b) adding
a fluxing agent to the melt; (c) adjusting the temperature of the
melt together with the fluxing agent such that the components or
salts thereof melt and at the same time the powder to be produced
crystallizes out, so that monocrystalline powder grains grow; and
(d) cooling the melt such that the growth of the monocrystalline
powder grains is stopped. The present invention also relates to a
monogram membrane comprising monocrystalline copper indium
diselenide or GaAs grains produced according to the above-described
process.
DETAILED DESCRIPTION OF THE INVENTION
According to the process, a melt is formed and a fluxing agent is
added. The melt is formed from the individual components of a
semiconductor material, preferably a II/VI or III/V semiconductor,
an example of which can therefore be the components of copper
indium diselenide or GaAs. Salts containing the components can also
be fused instead of the components. The components or their salts
are preferably chosen such that the components are present in the
melt in the same stoichiometric composition as that of the powder
to be produced.
The melt must then be brought to a temperature at which the
individual components or their salts become fused and at the same
time the powder to be produced crystallizes out. Such a temperature
typically lies between 300.degree. C. and 1000.degree. C. In the
appropriate temperature range, monocrystalline powder grains are
formed in the melt. Once the powder grains have reached the desired
size, the melt is cooled or quenched so rapidly that the growth of
the powder grains is stopped as a result. The appropriate instant
of quenching, as well as the appropriate temperature profile for
obtaining desired powder sizes are determined by, for example,
preliminary experiments. After quenching or cooling it is expedient
to eliminate the fluxing agent.
The process is simple and inexpensive, since it is not necessary to
produce large single crystals beforehand. The grains grow
uniformly, and so the resulting powder comprises grains of uniform
size.
To produce copper indium diselenide monocrystalline powder, the
salt melt can be formed from CuSe and In, or from Cu, Se and In, or
from Cu--In alloys and Se, or from Cu, In or Se salts with
appropriate melting points. A typical melt then has the composition
of, for example, 6.35 g Cu, 11.5 g In, 15.8 g Se and 40 vol %
CuSe.
NaCl or an excess of Se or selenides can be used as a fluxing agent
in a melt containing copper indium diselenide. The proportion of
fluxing agent typically amounts to 40 vol % of the melt. In
general, however, it can range between 10 vol % and 90 vol %. The
melt together with the fluxing agent is introduced into, for
example, a quartz ampoule. The quartz ampoule is evacuated and
fused. Thereafter the quartz ampoule together with the contents
cited as an example is heated to at least 300.degree. C.,
especially 600.degree. C. As soon as the components have melted,
monocrystalline copper indium diselenide grains begin to grow. The
growth of a semiconductor such as copper indium diselenide takes
place as a function of time and of the fluxing agent used.
Depending on fluxing agent and desired size of the powder grains, a
treatment time ranging from 5 minutes to 100 hours is
necessary.
In order to stop the growth selectively, the melt is cooled. The
cooling rate determines the fault content and fault type in the
material, as well as the surface morphology. Quenching can be
completed within a few seconds. The melt can also be cooled over a
period of several hours. For this purpose the quartz ampoule
together with the contents can be cooled in a water bath or in air
at an instant determined by preliminary experiments. Thereafter the
contents are removed from the quartz ampoule and the fluxing agent
is eliminated. In the case of NaCl, this can be achieved, for
example, by dissolving the NaCl in water, provided the powder
grains are insoluble in water, as is the case of copper indium
diselenide. If Se is used as the fluxing agent, it can be
eliminated by volatilization of Se.
The temperature range in which recrystallization takes place
depends on the fluxing agent and the desired grain size, and can
lie between 100.degree. C. and 1000.degree. C. The process has been
used to produce, among other substances, monocrystalline copper
indium diselenide powder with extremely high electrical
conductivity. Grain diameters of 40 .mu.m, for example, have been
obtained. Grains with resistance of 10 to 30.OMEGA. have been
achieved. These values correspond to specific electrical
resistivities of 0.1 to 0.6 .OMEGA.m.
It was possible to produce powders with diameters of 0.1 .mu.m to
0.1 mm.
From the powders produced according to the process, there can be
produced by the prior art described hereinabove in the background
of the invention monogram membranes which can be used, for example,
in photovoltaics. A minimum diameter of 10 .mu.m was necessary for
production of monogram membranes, since otherwise a continuous
polymer film was not possible. A diameter of 50 .mu.m should not be
exceeded for the production of monogram membranes, since otherwise,
in the art of photovoltaics, for example, undesirably high series
resistances develop and material is wasted. It is worth emphasizing
that the grain sizes produced according to the process vary only
slightly within a batch.
Further examples of semiconductor materials from which
monocrystalline powders can be produced according to the process
are CdTe, CdSeTe, CdS, CdSSeTe, GaAs, InP.
* * * * *